The present invention relates to cementing operations, and more particularly, to cement compositions that comprise a copolymer retarder that comprises olefinically unsaturated non-acrylate sulfonate monomers and olefinically unsaturated carboxylic acid monomers and associated methods.
Cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of a pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
These cementing operations generally occur under a wide variety of well bore conditions, for example, ranging from shallow wells (less than about 1,000 feet) to extremely deep wells (greater than about 35,000 feet). Generally, the cement composition should remain in a pumpable state until the cement composition has been placed into the desired location. To retard the set time of the cement composition, among other things, so that the cement composition may be placed in a desired location, conventional set retarder compositions have been included therein. As used herein, the phrase “conventional set retarder compositions” refers to a wide variety of compositions commonly used in cementing operations for delaying the set time of a cement composition, including lignosulfonates, organic acids, phosphonic acid derivatives, synthetic polymers (e.g., copolymers of 2-acrylamido-2-methylpropane sulfonic acid (“AMPS”) and unsaturated carboxylic acids), inorganic borate salts, and combinations thereof. As used herein, the term “copolymer” refers to a polymer comprising two or more different monomers. As bottom hole circulating temperatures (“BHCT”) increase, combinations of conventional set retarder compositions have been used. For example, in well bores having a BHCT greater than about 200° F. to about 250° F., combinations of low temperature retarders, for example lignosulfonates and synthetic polymers, with co-set retarders such as organic acids and inorganic borate salts have been used. However, even such optimized combinations of conventional set retarder compositions may not provide a desired level of set retardation, for example, in wells having a bottom hole circulating temperatures (“BHCT”) above about 400° F. or in the range of from about 400° F. to about 600° F. Therefore, these temperatures limit the temperatures at which a cement composition may be pumped using conventional set retarder compositions and, thus, limit the depths and associated temperatures at which well bores may be drilled and isolated with a cement composition placed in the annulus.